07 Class Diagrams

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UML Class Diagram

and PackagesWritten by

Zvika GuttermanAdam Carmi


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UMLClass Diagrams 2

Agenda What is a Class Diagram?

Essential Elements of a UML Class

Diagram

Packages and Class Diagrams

Analysis Classes Approach

Tips


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UMLClass Diagrams 3

What is a Class Diagram?

A class diagram describes the types ofobjects in the system and the various kinds

of static relationships that exist amongthem.

A graphical representation of a static view ondeclarative static elements.

A central modeling technique that runsthrough nearly all object-oriented methods.

The richest notation in UML.


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UMLClass Diagrams 4

Essential Elements of a

UML Class Diagram Class

Attributes

Operations Relationships

Associations

Generalization

Dependency

Realization

Constraint Rules and Notes


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UMLClass Diagrams 5

Classes A class is the description of a set of objects

having similar attributes, operations,

relationships and behavior.

Window

size: Size

visibility: boolean

display()

hide()

Class

Name

Attributes

Operations


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UMLClass Diagrams 6

Associations A semantic relationship between two or moreclasses that specifies connections among theirinstances.

A structural relationship, specifying that objects ofone class are connected to objects of a second(possibly the same) class.

Example: An Employee works for a Company

CompanyDepartmentEmployee


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UMLClass Diagrams 7

Associations (cont.) An association between two classes

indicates that objects at one end of an

association recognize objects at the other

end and may send messages to them.

This property will help us discover less trivial

associations using interaction diagrams.


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UMLClass Diagrams 8

Associations (cont.)

StaffMember Student1..* *instructs

instructor

Association

name

Role

name

MultiplicityNavigable

(uni-directional)

associationCourses

pre -requisites

0..3Reflexive

association

Role

*


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UMLClass Diagrams 9

Associations (cont.) To clarify its meaning, an association may be

named.

The name is represented as a label placed midwayalong the association line.

Usually a verb or a verb phrase.

A role is an end of an association where itconnects to a class.May be named to indicate the role played by the class

attached to the end of the association path. Usually a noun or noun phrase

Mandatory for reflexive associations


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UMLClass Diagrams 10

Associations (cont.) Multiplicity

The number of instances of the class, next to

which the multiplicity expression appears, thatare referenced by a single instance of the classthat is at the other end of the association path.

Indicates whether or not an association is

mandatory. Provides a lower and upper bound on the

number of instances.


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Associations (cont.)Multiplicity Indicators

Exactly one 1

Zero or more (unlimited) * (0..*)

One or more 1..*

Zero or one (optional association) 0..1

Specified range 2..4

Multiple, disjoint ranges 2, 4..6, 8


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Aggregation A special form of association that models a

whole-part relationship between an

aggregate (the whole) and its parts.

Models a is a part-part of relationship.

Whole Part

Car Door House1..*2..*


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Aggregation (cont.) Aggregation tests:

Is the phrase part of used to describe the relationship? A door is part of a car

Are some operations on the whole automaticallyapplied to its parts?

Move the car, move the door.

Are some attribute values propagated from the whole toall or some of its parts?

The car is blue, therefore the door is blue.

Is there an intrinsic asymmetry to the relationshipwhere one class is subordinate to the other?

A door ispart of a car. A caris notpart of a door.


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Generalization Indicates that objects of the specialized

class (subclass) are substitutable for objects

of the generalized class (super-class).

is kind of relationship.

Shape{abstract}

Circle

Super

Class

Sub

Class

An abstract

class

Generalizationrelationship

{abstract} is a

tagged value that

indicates that the

class is abstract.The name of an

abstract class should

be italicized


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Generalization A sub-class inherits from its super-class

Attributes

Operations

Relationships A sub-class may

Add attributes and operations

Add relationships

Refine (override) inherited operations A generalization relationship may notbe used to

model interface implementation.


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Dependency A dependency indicates a semantic relation

between two or more classes in which a change in

one may force changes in the other although thereis no explicit association between them.

A stereotype may be used to denote the type of the

dependency.

Iterator Vector


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Realization

A realization relationship indicates that one

class implements a behavior specified by

another class (an interface or protocol).

An interface can be realized by many

classes.

A class may realize many interfaces.

LinkedList

ListLinkedList List


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UML

Class Diagrams 19

ConstraintRu

les and Notes Constraints and notes annotate among otherthings associations, attributes, operations and

classes.

Constraints are semantic restrictions noted asBoolean expressions.

UML offers many pre-defined constraints.

id: long { value > 0 }

Customer

Order*1 { total < $50 } may becanceled

Constraint Note


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UML

Class Diagrams 20

TVRSEx

ample

id : longname : Stringrank : int

Policeman

TrafficPoliceman id : long

description : String

TrafficReport

id : longdescription : String

Violation

name : String

id : long

Offender

1..* 1

reports of

1..*

issues1 *

occuredAt : Date


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UML

Class Diagrams 21

UML Packages A package is a general purpose groupingmechanism.

Can be used to group any UML element (e.g. use case,

actors, classes, components and other packages. Commonly used for specifying the logical

distribution of classes.

A package does not necessarily translate into a

physical sub-system. Name


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UML

Class Diagrams 22

Logical Distribution of

Classes Emphasize the logical structure of the

system (High level view)

Higher level of abstraction over classes.

Aids in administration and coordination of the

development process.

Contributes to the scalability of the system. Logical distribution of classes is inferred

from the logical architecture of the system.


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UML

Class Diagrams 23

Packages and Class

Diagrams (cont.) Add package information to class diagrams

A

DE

F

G

C

B


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UML

Class Diagrams 24

Packages and Class

Diagrams (cont.) Add package information to class diagrams

a.A

b.b.Db.b.E

b.a.F

b.a.G

a.C

a.B

b.a

b.b

ab


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Analysis Classes A technique for finding analysis classes

which uses three different perspectives of

the system: The boundary between the system and its actors

The information the system uses

The control logic of the system


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Boundary Classes Models the interaction between the systems

surroundings and its inner workings

User interface classes

Concentrate on what information is presented to the

user Dont concentrate on user interface details

Example:

ReportDetailsForm

ConfirmationDialog System / Device interface classes

Concentrate on what protocols must be defined.

Dont concentrate on how the protocols are

implemented


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Entity Classes

Models the key concepts of the system

Usually models information that is

persistent

Contains the logic that solves the system

problem

Can be used in multiple behaviors

Example: Violation, Report, Offender.


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Control Classes Controls and coordinates the behavior of the

system

Delegates the work to other classes

A control class should tell other classes to do

something and should never do anything exceptfor directing

Control classes decouple boundary andentity classes

Example: EditReportController

AddViolationController


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TVRSEx

ample

Vi l ti

E it rt tr ll r tr l

r f f i rt

f f r r f f i li

l r

rt t il F r

ry

f ir ti i l

ry

li B r xy

ry

f f r B r xy

ry

f f r B

li B


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Tips

Dont try to use all the various notations.

Dont draw models for everything,

concentrate on the key areas.

Draw implementation models only when

illustrating a particular implementation

technique.

07 Class Diagrams

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